diff --git a/separate_rects.h b/separate_rects.h
index de8b660..cb46ecb 100644
--- a/separate_rects.h
+++ b/separate_rects.h
@@ -105,6 +105,14 @@
     bitset &= ~(((TUInt)1) << id);
   }
 
+  void subtract(TId start, TId end) {
+    if (start > end)
+      return;
+    TId start_mask = (1 << start) - 1;
+    TId end_mask = (1 << end) - 1;
+    bitset &= ~(start_mask ^ end_mask);
+  }
+
   bool isEmpty() const {
     return bitset == 0;
   }